Professional photographers make their livelihood by capturing valuable images of great interest that others have not captured. Their financial reward often depends upon their exclusive possession of those images. This requires care that their images not fall into the hands of their competitors, for example, through theft of their camera or theft of the storage medium (e.g., a digital disk) on which the valuable images have been stored. As one possible example, an electronic transmission via the internet of the photographer's valuable images from a remote location to his publisher can be intercepted by another publisher or competitor who then uses those images. In such a case, the value of the photographer's own images is reduced, since the images are no longer exclusively possessed or sold by his publisher.
As another example, the photographer may have caught a criminal on camera, and government authorities may confiscate the camera and storage media (film or disk) pursuant to a criminal investigation. In such a case, the government authorities have no need to deal with the photographer, as they can develop or print the images themselves without assistance from the photographer. The authorities therefore need not return the camera or the film/disk to the photographer, regardless of the financial impact such a loss places on the photographer.
As a further example, the photographer may be an amateur who wishes to maintain his images in complete secrecy, and is therefore forced to take drastic steps to prevent any theft of his camera or its film or disk.
One possibility might be for the photographer to use a digital camera that captures each still image as video data, and to first encrypt the video data before storing or recording it on storage media (a removable diskette) in the camera. This would frustrate attempts to steal the images by copying them from the encrypted data. Thus, someone who steals the diskette or who intercepts a transmission (e.g., on the internet) of the encrypted image, would not be able to see the photographers' images. The photographer would ensure that his publisher possesses the encryption key used in the camera to encrypt the images as recorded on the camera diskette. The publisher would use the key to de-encrypt each of the received images.
Such an approach is not practical. First, the digital camera would necessarily require circuitry to electronically store the encryption key in a retrievable form and circuitry to encrypt each block of video data with the encryption key. Secondly, theft of the camera would compromise the key, since the encryption circuitry within the camera must contain or store the encryption key in order to function. Such a theft would therefore allow an unauthorized person possessing the camera and skilled in extracting the key from the camera to decrypt the video data stored on the diskette (or any other video data recorded by that camera). Third, if the encryption key were compromised secretly by some other means not involving the camera (so that the camera continues to be used), every image ever encrypted and recorded by that camera, whether in the past or in the future, would be compromised. Many opportunities for stealing the encryption key can arise. For example, generation of the encryption key (e.g., by a random number generator) must involve a number of persons, including those responsible for generating keys, those who assign keys to certain cameras and load the keys to the cameras, and a documentation system (presumably held at a safe location) correlating different cameras with their different encryption keys for later decryption of images received from various photographers. Thus, the camera user must always consider the possibility that, unbeknownst to him, the encryption key may have fallen into the wrong hands either through his negligence or that of his publisher (who must also have the same key or a related key). This would compromise all of the images taken with the camera during the life of the camera. From the foregoing it can be seen that another disadvantage of an encrypting digital camera is that an elaborate set of precautionary procedures must be employed in the administration of the encryption key and any related keys. Mathematically related encryption keys capable of decrypting the same encrypted data are often distinguished as “public” and “private” keys, in which one is disseminated while the other is not. All such schemes involve a significant risk that the key may be compromised at any time without the knowledge of the authorized users.
A further disadvantage of an encrypting digital camera is that the presence inside the camera of circuitry storing an elaborate encryption key and related encrypting apparatus could alert a skilled thief in possession of the camera that any seemingly innocent noise present on the camera's diskette or memory may actually contain valuable video data retrievable via decryption, thus motivating the thief to search for the encryption key either in the camera or through another theft involving the encryption key administration documentation at the supposedly secure location.
Thus, it has not seemed practical or possible to implement a fool-proof encrypting digital camera.